Crimpable composite polyamide yarn

ABSTRACT

A crimpable bicomponent filament in which one component is a polyamide and the other a random copolyamide containing specified percentages of three polymeric units. The different units and their concentrations are 70-82 percent hexamethylene adipamide, 13-25 percent caproamide and 5-17 percent hexamethylene dodecanedioamide. Yarns of one or more such filaments are particularly useful in the manufacture of hosiery because of their high crimpability, high strength and low shrinkage in the fabric.

United States Patent Ben et a1. 1 1 June 6, 1972 [54] CRIMPABLECOMPOSITE POLYAMIDE 3,526,571 9/1970 Ogata ..264/D1G. 26 YARN 3,418,19912/1968 Anton... .161/173 3,399,108 8/1968 Olson ..161/173 Inventors:Victor Ralph Ben, Wilmington, DeL; Peter Steven Kay, Martinsville, Va.

[73] Assignee: E. 1. du Pont de Nemours and Company,

Wilmington, Del.

[22] Filed: May 1, 1970 21 App1.No.: 33,955

[52] U.S.Cl ..57/140BY,28/72.17, 161/173, 264/171 [51] Int. Cl. ..D02g3/02 [58] Field ofSearch ..161/l73, 175, 177; 260/78 A, 260/78 L; 57/140R, 140 BY; 264/D1G. 26; 28/72.]?

[56] References Cited UNITED STATES PATENTS 3,554,980 l/197I Ando et a1..264/176 F 3,322,731 5/1967 Cook et al ..260/78 L PrimaryExaminer-Robert F. Burnett Assistant Examiner-Linda C. KoeckertAtt0rneyJ. R. McGrath [57] ABSTRACT A crimpable bicomponent filament inwhich one component is a polyamide and the other a random copolyamidecontaining specified percentages of three polymeric units. The differentunits and their concentrations are 70-82 percent hexamethyleneadipamide, 13-25 percent caproamide and 5-17 percent hexamethylenedodecanedioamide. Yarns of one or more such filaments are particularlyuseful in the manufacture of hosiery because of their high crimpability,high strength and low shrinkage in the fabric.

5 Claims, No Drawings This invention relates to composite filaments andparticularly to improved composite filaments prepared from syntheticlinear polyamides.

Synthetic polyamide filaments and yarns have been predominant in thewomens hosiery market for many years. In this market, there is now anincreasing demand for the socalled stretch hose. Hose of this type'aremuch smaller than conventional hose but have the ability to stretch muchmore and thereby provide improved fit as well as reducing the number ofsizes of hose required to fit the range of leg sizes normallyencountered.

Composite filaments which are particularly suitable for the productionof stretch hosiery were disclosed by Olson in US. Pat. No. 3,399,108.These filaments have the ability to crimp under restraint and this leadsto distortion of the stitches in the hosiery fabric so that the fabrichas more ability to stretch than a conventional hosiery fabric. Althoughthese composite filaments-have produced good stretch hose, furtherimprovements in crimpability under fabric restraint are desirable,particularly in the production of miniature stretch hose. In thisconnection, the current wide-spread use of pantyhose also makesimprovement in the crimpability of multifilament welttype yarns verydesirable. in addition, improvement in filament strength is desirable inorder to enhance the durability of hosiery leg yams;

SUMMARY OF THE INVENTION It is the principal object of this invention toprovide a composite polyamide filament having an improved balance ofcrimp characteristics and strength. Other objects will become apparentfrom the description and examples to follow.

The above object is accomplished by a crimpable composite filamenthaving a crimp elongation, when subjected to steam at 100. C. under aload of 1.2 milligrams/denier (mgd), greater than 30 percent andconsisting of two continuous, adherent, eccentrically arranged,synthetic, polyamide components, one component consisting essentially ofa homopolyamide and, the other component consisting essentially of arandom copolyamide containing at least 70 percent by weight ofhexamethylene adipamide units. The copolyamide is characterized by anamide group frequency of 8440-8725 equivalents/10 grams and adifferential thennal analysis (DTA) melting point of 210-225 C.Preferably, the homopolyamide ispo1y(hexamethylene adipamide) i.e., 6--6 nylon, or poly(epsilon-caprolactam), i.e., 6 nylon; and thecopolyamide is a copolymer consisting essentially of 70-82 percent byweight of 6-6 nylon polymer units, 1 3-25 percent by weight of 6 nylonpolymer units and 5-17 percent by weight of hexamethylenedodecanedioamide (6-12 nylon) polymer units.

The crimp diameter, i.e., the average diameter of the helices formedwhen the filament is subjected to steam at 100 C. under a load of 1.2mgd, is preferably less than 6 mils and most desirably in the range of3-5 mils.

The copolymer employed should contain at least 70 percent by weight of6-6 polymer units to provide a high level of strength and durability inhose. The other components of the copolymer should be selected to give aDTA melting point no greater than 225 C. so that the copolymer componentof the as-drawn filament will have adequate shrinkage to produce highlevels of crimp. The DTA melting point should be at least 210C. toprovide adequate shrinkage tension for crimp formation under restraintand to insure a high tenacity. The

amide group frequency should be in the range of 8440-8725 equivalents]10' gms. of polymer since lower levels lead to inadequate crimpabilityand higher levels lead to undesirable moisture sensitivity and loss offit athigh humidity.

The filaments of this invention are prepared by extruding thehomopolyamide and copolyamide in either a side-by-side or a sheath-corerelationship to form a filament (or two or more filaments as a yam),quenching and drawing the filament in the conventional manner, passingthe drawn filament through a heating zone under low tension to developcrimp and thereafter stretching the filament to remove crimp. Afterpassing through the heating zone, the crimped filament should bepennitted to cool before crimp is removed. The temperature in theheating zone should be at least C. to give the desired crimpcharacteristics. The temperature required will, of course, dependon thelength of the heating zone and the speed of the filament passing throughthe zone.

The preferred technique for reducing tension in the heating zone andthen removing crimp is by passage of the precrimped filament over aseries of snubbing pins in its advance away from the draw roll, asuitable heating means such as an air jet being interposed between thedraw roll and snubbing pins, as shown, for example, in FIGS. 1 and 4 ofthe Olson patent. From the snubbing pins, the filament passes around apowerdriven roll, rotating at a lower peripheral speedthan the draw rollto permit the filament to retract between 'the rolls. The

degree of retraction permissible will depend on the amount of shrinkage,independent of crimping, which occurs between the two rolls. This, inturn, will depend to a considerable extent on the temperature in theheating zone. Generally, a high degree of snubbing is desired to providevery low tension and maximum shrinkage in the heating zone. 7

In the extrusion of sheath-core filaments, the homopolyamide ispreferably extruded as the sheath to facilitate quenching of thefilaments. Use of the copolyamide as a sheath results in slowerquenching and can lead to filament sticking at high spinning speeds.

The two components are usually present in approximately equal amounts byweight of the filamentsghowever, the ratio may be varied as required toachieve the desired properties. With sheath-core filaments, it may bedesirable to employ a somewhat larger percentage of the higher shrinkagecomponent in the core. v

ln producing sheath-core filaments, the core should be highly eccentricin order to develop the required retractive force on crimping. Thismeans that part of the sheath will be very thin, i.e., the minimumthickness of the sheath will range from 5 percent of the filamentdiameter to 0. l percent or less.

Either or both of the components may contain any of the variousadditives commonly employed in the production of fibers, such asdelusterants, pigments, dyes, antioxidants, antistatic agents andsurface-modifying agents.

In addition to the exemplified yarns, other deniers and other filamentcounts may be employed. Although hosiery filaments are usually of roundcross section, other shapes may be employed and may be particularlyuseful in certain end uses such as in tricot knit fabrics or certainwoven fabrics. For such'purposes, cross sections of trilobal shape,shield shape, heart shape, cruciform shape and various multilobalconfigurations may be employed.

The filaments and yarns of this invention possess an unusually goodbalance of desirable crimp characteristics, high strength and lowshrinkage in the fabric. While certain copolymer compositions outsidethe-limits of this invention may be processed to give almost equivalentcrimp characteristics, this is accomplished only at the expense of aloss in strength, particularly afier boil-off as in a finished hose. Inaddition, the filaments of this invention have the desirablecharacteristic of being essentially straight when removed from thepackage but tend todevelop crimp readily afterknitting due to themechanical working of the filament inthe knitting machine. This resultsin a reduction in area of the greige fabric and, as a consequence, fewerpicks develop in the hose during mill handling. Picks are flaws in thestitch construction and may be slight distortions of the stitch whichcan be corrected by pulling a wale or course or they may be severedistortions which are more difficult to repair.

Surprisingly, the shrinkage of the filaments of this invention issubstantially lower than that of prior art bicomponent hosieryfilaments. Shrinkages below 4' percent are readily achieved. Thispermits the knitting of a tighter fabric which is less subject topicking and is appreciably more economical in terms of yarn required toprovide any given size of hose.

It has also been found that satisfactory miniature hose may be made fromthe readily crimpable filaments of this invention without the addedsteaming operation which has been required in the past for bicomponentfilament stretch hose.

The expression relative viscosity" as used herein signifies the ratio offlow time in a viscometer of a polymer solution containing 8.2 percentby weight of polymer, relative to the flow time of the solvent byitself. Measurements of relative viscosity are made with 5.5 grams ofpolyamide in 50 milliliters of 90 percent by weight formic acid at 25 C.

Shrinkage and crimp elongation of the filament are determined asfollows:

A 750 denier skein of monofil or multifilarnent yarn is prepared bywinding the requisite number of turns on a reel to give a skein of about55 centimeters length when suspended with a weight attached. The denierof the filament bundle representing the collapsed skein will, of course,be twice that of the original skein, i.e., 1,500 denier. The skein ishung on a hook with a 500 gm. weight suspended from its other end. Afterone minute, the length (a) of the skein is measured. The 500 gm. loadisremoved and a 1.8 gm. load is applied in its place so that the skein isunder a tensile load of 1.2 mg./den. (mgd), i.e., a tension slightly inexcess of that on the yarn when knitted into a fabric. The skein withthe weight attached is subjected to 100 C. steam at atmospheric pressure(hereinafter referred to as atmospheric steam") for one minute, afterwhich the skein is allowed to dry in air for minutes. The skein length(b) is then measured. The 1.8 gm. load is then removed, the 500 gm. loadis again applied for one minute, and the length (c) of the skeindetermined. The crimp elongation and shrinkage of the filament arecalculated from the following equations:

Crimp Elongation, 100

Shrinkage, =100 T c values reported herein. Most polymers, andparticularly copolymers, melt over a temperature range depending on theheating rate. In this determination, the melting point is taken as thepeak temperature in the endothermic temperature plot. Due to the factthat polymer melting temperatures are usually not sharp, the accuracy ofthis measurement is 1 2 C. The polymer sample may be in the form offlakes, chips, fiber or film. In the following examples, the polymersamples were in the form of flakes or fiber. Using the instructionsprovided with the commercial Du Pont instrument, the conditions used tomake the measurements are as follows:

Reference Aluminum Pan Program Mode Heating Heating Rate l2 C./min.

Atmosphere Nitrogen, 6 min.

T Scale 50 C./in.

ATScale 0.lC./in.

Amide group frequency is calculated as follows: Homopolyamides I a. AABBpolymers (e.g., 6-6 or 6-12 nylons) where F =Amide Frequency W, =Grammolar weight of polyamide repeat unit.

2 X 10 s-u 310 64-50 b. AB polymers (i.e., 6 nylon) 10 F Wm 6 Thus. F

8850 (same as for 6-6) EXAMPLE I evaporator is charged with an aqueoussolution containing 257 pounds 1 16.6 kg.) of hexamethylenediammoniumdodecan edioate (6-12 nylon salt), 2034 pounds (922.6 kg.) ofhexamethylenediammonium adipate (6-6 nylon salt) and 338 pounds (153.3kg.) of epsilon caprolactam, and the resulting solution is heated at34.7 psig (3.4 atmospheres) until the temperature reaches 146 C., givinga salt concentration of approximately 76 percent. The solution is thentransferred to an autoclave, heated to a temperature of about 205 C. andbrought to a pressure of 250 psig l8 atmospheres). At this point,sufficient 20 percent aqueous titanium dioxide slurry is added to give adelusterant concentration of 0.3 percent TiO, in the final copolymer.The solution is then heated at 250 water and cut into flake. Thecopolymer, consisting by weight of 75 percent polyhexamethyleneadipamide, 15 percent polyepsilon caproamide and 10 percentpolyhexamethylene dodecanedioamide, has a relative viscosity of 46.

Polyhexamethylene adipamide (6-6 nylon) flake having a relativeviscosity of 46.5 is prepared in the conventional manner. The two flakes(6-6 and 6-6/6/6-12) are first conditioned by exposure to humidifiednitrogen at l25 C. and 145 C., respectively, and then melted and pumpedto a spinneret assembly of the type shown in FIG. 3 of 11.8. Pat. No.3,399,108 to Olson, with holes arranged to spin three filament yarns.'lhe relative viscosity of the 6-6 polymer after conditioning is 50 andthat of the 6-6/6/6-l2 copolymer flake is 56. The two polymers areextruded, with the copolymer a the core to form eccentric sheath-corethree-filament hosiery yarns containing 58 percent of the randomcopolymer and 42 percent by weight of the homopolymer. The sheath, atits thinnest point, has a thickness equivalent to about 1 percent of thetotal filament diameter. The clearance between the projection and plate1420f Olson is 0.003 inch (0.076 mm.). The

filaments are set by quenching, using a 60 inch (152 cm.) chimney and anair temperature of 60 C., steam conditioned as described by Babcock inU.S. Pat. No. 2,289,860 and wound into a package at 546 ypm. The yarn issubsequently withdrawn from the package and drawn at a ratio of 4.47over an unheated draw pin situated between feed and draw rolls to give afinal denier of 23-24 (nominally 20-3). It is then passed from the drawroll at 5 84 yprn (5 33 meters/min.) through a 3- inch long (7.6 cm.)tubular crimping chamber of the type shown in FIG. 5 of the Olsonpatent. The yarn is heated by passing 1.05 cubic feet/minute (0.03 cu.meter/min.) of 278 C. air through the chamber to give an air temperatureof 188 C. at the exit.

The yarn is then passed over two snubbing pins, the total yarn contactwith the pins being 390, then to a withdrawal roll and finally to awinding device. The snubbing pins act to reduce the speed of the yarn inthe heating zone so that the components can shrink differentially andthe filaments can crimp under the influence of the heat. In addition,the yarn is stretched sufficiently between the pins and the withdrawalroll to remove most of the crimp. Between the draw and withdrawal rolls,the yarn is permitted to retract by 40 percent of its as-drawn length.

When the crimpable yarn is exposed to hot water or steam, it crimpsagain in a very uniform fashion, and the crimp diameter and crimpelongation are quite uniform. The crimp elongation at a load of 1.2 mgd,determined as described previously, is 38 percent in atmospheric steam.The average crimp spacing and diameter are about 22 mils (0.56 mm.) and4.6 mils (0.12 mm.), respectively. The shrinkage of the yarn is 1.6percent. The tenacity of yarn removed from finished hose is 4.2 gpd.

EXAMPLE II 20 denier, three-filament yarn with a crimp elongation of 40percent, prepared substantially as described in Example I, was used asthe leg yarn in conventional knitting of womens hose. For comparison,otherwise identical hose were knit from 20 denier, three filament yarnprepared from the composition described below in the last paragraph ofExample III. It was observed that greige hose from the yarn of thisinvention were substantially smaller than the comparison hose afterremoval from the knitting machine due to a tendency for the filaments tocrimp at this stage. This reduction in size leads to a reduction inpicks during subsequent handling of the hose in the mill. When the abovetwo types of hose are tested for picking propensity by tumbling greigehose for six minutes in a drum lined with pins designed to produce picksat a rapid rate, the number of picks produced in 12 hose of the yarn ofthis invention is 101 compared to 226 for 12 of the comparison hose. Inaddition, it was found, however, that the tumble steaming operationcould be eliminated for the hose from the readily crimpable yarn of thisinvention since the crimp development during the normal scouring anddyeing operation was sufiicient. When hose from the yarn of thisinvention, without tumble steaming, is scoured at 150 F. (65.6 C.) or212 F. 100 C.) for 15 minutes, followed by a standard dye cycle at 180F. (82.2 C.) for 90 minutes, the'average over-all length of theunboarded hose was approximately 19 inches (48 cm.), and the length ofthe leg portion was approximately 15 inches (38 cm. The average over-alllength of the comparison hose with tumble steaming was about 21 inches(60 cm.), and the leg length was 17 (50 cm.) inches.

EXAMPLE Ill A copolymer flake containing 75 percent by weight ofhexamethylene adipamide polymer units, 15 percent epsilon caproamideunits and 10 percent hexamethylene dodecanedioamide units and having arelative viscosity of 55 .9 is prepared following the general procedureof Example I.

The copolymer flake and 66 nylon polymer flake having a relativeviscosity of 50.1 are extruded from a spinneret of the type identifiedin Example 1 to form a sheath-core filament with the copolymer as thecore and having a final denier of about 15. The monofil, consisting ofabout 60 percent core and 40 percent sheath by weight, is air-quenchedand wound into a package. The filament is then removed from the packageand drawn at a ratio of 5.02 over an unheated pin at a draw rollperipheral speed of 850 yds./min. (776 nieters/minute). From the drawroll, the filament is passed upwardly through a tubular crimping chamberof the type shown in FIG. 5 of the Olson patent, over achange-of-direction guide, downwardly to a series of snubbing pins of3/16 in. (4.77 mm.) diameter and over a power-driven withdrawal rollrotating at a peripheral speed of 527 yds./min. (482 meters/min.) to awinding device where the filament is wound into a package in the usualmanner. In the crimping device, the filament is heated by astream of airwhich is passed into the jet at a temperature of 295 C.

Filaments designated A and B in Table l are prepared with differentamounts of snubbing. Withdrawal roll speed is somewhat higher forfilament B, as' indicated by the lower extent of retraction. Thecumulative snubbing angle, i.e., the sum of the angles of contact withthe individual pins, is reported in Table l. Crimp characteristics andtensile properties of the filaments are also reported in Table 1. i

For comparison, filaments are prepared substantially as was filament Bexcept that the core is a copolymer prepared substantially as in ExampleVIII of Olson by combining a 49.5 percent by weight 6-6 salt solutioncontaining 1,362 lbs. of dry salt, a 26 percent by weight 6-12 saltsolution containing 486 lbs. of dry salt and a 31 percent by weight 6-10salt solution prepared with technical grade sebacic acid and containing833 lbs. of dry salt. The draw ratio is adjusted to give approximatelythe same elongation at breakas the filaments of this invention. The airtemperature at the crimping chamber is also slightly lower since thistemperature was more nearly optimum for polymer composition. Thesefilaments are designated C and D in the following table.

TABLE I Filament A B C D Draw Ratio 5.02 5.02 4.74 4.74 Snubbing,Cumulative Angle 245 1025 245 1025 Retraction*, 38 28 28 28 Crimping.let Inlet Air Temp., C. 295 295 280 280 Crimp Elongation, 58 71 41 63Crimps/Inch,

Extended, 0.3 g.p.d.

load 29.0 37.8 28.5 41.6 crimps/cm, Extended,

0.3 g.p.d. load 1 1.4 14.9 1 1.2 16.4 Shrinkage, 3.0 3.7 5.3 4.6 CrimpPitch, Mils 22.2 15.1 25.5 14.6 Crimp Pitch, mm. 0.565 0.384 0.648 0.371Crimp Dia., Mils 7.1 4.3 7.9 4.4 Crimp Dia., mm. 0.180 0.109 0.200 0.112 Tenacity, gpd. 5.3 5.1 4.4 3.8 Elongation 43 45 45 50 Tenacity, gpd,After Boil-ofi' 4.5 5.1 3.9 3.3 Elongation 42 44 I 45 38 DTA MeltingPoint,

C., copolyamide 219 219 207 207 Amide Freq., EquivJ 10 grams,

copolyamide 8595 8595 7840 7840 'Retraction of filament between drawroll and withdrawal roll based on peripheral speeds of rolls.

" Elongation at break EXAMPLE 1V Women's seamless hose are knit in theconventional manner using denier monofil prepared substantially asdescribed in connection with filaments C, D and B in Example 111. It wasnoted that the greige hose as removed from the knitting machinewere muchsmaller in the case of filaments D and B as compared to hose fromfilament C. Table 2 records the relative areas of the knit hose tubingwhere the area of the hose from filament C is designated as 1.00. Thisreduction in fabric .area is due to the greater tendency of filaments Dand B to crimp after knitting. Although the relative area of the fabricfrom filament D is substantially reduced, this is accomplished only witha considerable (0.6 gpd) reduction in tenacity, as can be seen from acomparison of filaments C and D of Table Followingthe procedure ofExample 111, copolyamides of 6-6, 6 and 6-12 nylon having thecompositions shown in Table 3 were prepared and processed into 15 denierbicomponent monofilaments with 66 nylon as the sheath component, theprocessing conditions being substantially as in Example I. Table 3records the crimp elongation values for the three compositions, the 75:15:10 and 70:20:10 compositions being within the scope of this inventionwhile the 82:8:10 composition is for comparison.

TABLE 3 6-6/6/6-12 Composition weight I: 75:15:10 :20:10 82:8:10

Determined from phase diagram Having thus described the invention, whatis claimed as new and desired to be secured by Letters Patent is:

l. A readily crimpable yarn of at least one composite filament havingcontinuous, adherent, eccentric components, one component being apolyamide, the other arandom copolyamide containing 70-82 percent byweight of hexamethylene adipamide units, 13-25 percent by weight ofcaproamide units and 5-17 percent by weight of hexamethylenedodecanedioamide units.

2. The yarn of claim 1, said filament being characterized by a shrinkagein the fabric of less than 4 percent.

3. The yarn of claim 2, said filament, having an after boil-off tenacityof at least 4.0 grams/denier.

4. The yarn of claim 2, said copolyamide having a DTA melting point of210225 C.

5. The yarn of claim 2, said one component being polyhexamethyleneadipamide, said copolyamide containing the three different units in aratio of about :15:10.

2. The yarn of claim 1, said filament being characterized by a shrinkagein the fabric of less than 4 percent.
 3. The yarn of claim 2, saidfilament having an after boil-off tenacity of at least 4.0 grams/denier.4. The yarn of claim 2, said copolyamide having a DTA melting point of210*-225* C.
 5. The yarn of claim 2, said one component beingpolyhexamethylene adipamide, said copolyamide containing the threedifferent units in a ratio of about 75:15:10.